planner: add simple task stack for memo

pkg/planner/memo/BUILD.bazel

@@ -8,6 +8,7 @@ go_library(
         "group_expr.go",
         "implementation.go",
         "pattern.go",
+        "task.go",
     ],
     importpath = "github.com/pingcap/tidb/pkg/planner/memo",
     visibility = ["//visibility:public"],
@@ -27,10 +28,11 @@ go_test(
         "group_test.go",
         "main_test.go",
         "pattern_test.go",
+        "task_test.go",
     ],
     embed = [":memo"],
     flaky = True,
-    shard_count = 22,
+    shard_count = 24,
     deps = [
         "//pkg/domain",
         "//pkg/expression",

pkg/planner/memo/task.go

@@ -0,0 +1,78 @@
+// Copyright 2024 PingCAP, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package memo
+
+import (
+	"strconv"
+	"sync"
+)
+
+// Task is an interface defined for all type of optimizing work: exploring, implementing, deriving-stats, join-reordering and so on.
+type Task interface {
+	// task self executing logic
+	execute()
+	// task self description string.
+	desc() string
+}
+
+// TaskStackPool is initialized for memory saving by reusing taskStack.
+var TaskStackPool = sync.Pool{
+	New: func() any {
+		return newTaskStack()
+	},
+}
+
+// TaskStack is used to store the optimizing tasks created before or during the optimizing process.
+type TaskStack struct {
+	tasks []Task
+}
+
+func newTaskStack() *TaskStack {
+	return &TaskStack{
+		tasks: make([]Task, 0, 4),
+	}
+}
+
+func (ts *TaskStack) Len() int {
+	return len(ts.tasks)
+}
+
+func (ts *TaskStack) Pop() Task {
+	if !ts.Empty() {
+		tmp := ts.tasks[len(ts.tasks)-1]
+		ts.tasks = ts.tasks[:len(ts.tasks)-1]
+		return tmp
+	}
+	return nil
+}
+
+func (ts *TaskStack) Push(one Task) {
+	ts.tasks = append(ts.tasks, one)
+}
+
+func (ts *TaskStack) Empty() bool {
+	return ts.Len() == 0
+}
+
+type TestTaskImpl struct {
+	a int64
+}
+
+func (t *TestTaskImpl) execute() {
+
+}
+func (t *TestTaskImpl) desc() string {
+	return strconv.Itoa(int(t.a))
+}

pkg/planner/memo/task_test.go

@@ -0,0 +1,77 @@
+// Copyright 2024 PingCAP, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package memo
+
+import (
+	"testing"
+	"unsafe"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestTaskStack(t *testing.T) {
+	newSS := newTaskStack()
+	// size of pointer to TaskStack{}
+	require.Equal(t, int64(unsafe.Sizeof(newSS)), int64(8))
+	// size of pointer to TaskStack.[]Task, cap + len + addr
+	require.Equal(t, int64(unsafe.Sizeof(newSS.tasks)), int64(24))
+	// size of pointer to TaskStack's first element Task[0]
+	newSS.Push(nil)
+	newSS.Push(&TestTaskImpl{a: 1})
+	newSS.Push(nil)
+	v := unsafe.Sizeof(newSS.tasks[0])
+	require.Equal(t, int64(v), int64(16))
+	v = unsafe.Sizeof(newSS.tasks[1])
+	require.Equal(t, int64(v), int64(16))
+}
+
+func TestTaskFunctionality(t *testing.T) {
+	taskTaskPool := TaskStackPool.Get()
+	require.Equal(t, len(taskTaskPool.(*TaskStack).tasks), 0)
+	require.Equal(t, cap(taskTaskPool.(*TaskStack).tasks), 4)
+	taskStack := taskTaskPool.(*TaskStack)
+	taskStack.Push(&TestTaskImpl{a: 1})
+	taskStack.Push(&TestTaskImpl{a: 2})
+	one := taskStack.Pop()
+	require.Equal(t, one.desc(), "2")
+	one = taskStack.Pop()
+	require.Equal(t, one.desc(), "1")
+	// empty, pop nil.
+	one = taskStack.Pop()
+	require.Nil(t, one)
+
+	taskStack.Push(&TestTaskImpl{a: 3})
+	taskStack.Push(&TestTaskImpl{a: 4})
+	taskStack.Push(&TestTaskImpl{a: 5})
+	taskStack.Push(&TestTaskImpl{a: 6})
+	// no clean if, put it back
+	TaskStackPool.Put(taskTaskPool)
+
+	// require again.
+	taskTaskPool = TaskStackPool.Get()
+	require.Equal(t, len(taskTaskPool.(*TaskStack).tasks), 4)
+	require.Equal(t, cap(taskTaskPool.(*TaskStack).tasks), 4)
+	// clean the stack
+	one = taskStack.Pop()
+	require.Equal(t, one.desc(), "6")
+	one = taskStack.Pop()
+	require.Equal(t, one.desc(), "5")
+	one = taskStack.Pop()
+	require.Equal(t, one.desc(), "4")
+	one = taskStack.Pop()
+	require.Equal(t, one.desc(), "3")
+	one = taskStack.Pop()
+	require.Nil(t, one)
+}